Cellulose microfibril-reinforced polymers and their applications

ABSTRACT

Cellulose microfibril reinforced polyers, corresponding latices, powders, films and rods, and uses thereof. Polymer/cellulose composites are prepared using individualized cellulose microfibrils with a high form factor, e.g., tunicin microfibrils, as the reinforcement. For this purpose, reinforced latices consisting of a polymer latex and a stable aqueous suspension of said microfibrils are used. Said polymers have a wide variety of uses, particularly in paints and nanocomposites.

FIELD OF THE INVENTION

The present invention relates to polymer matrixes reinforced withcellulose fibers, to their production in the form of aqueoussuspensions, and to certain uses.

BACKGROUND OF THE INVENTION

Industry generally calls for composite materials consisting of a polymermatrix whose properties, in particular the mechanical properties, mustbe adapted by incorporation of fillers or reinforcements. Certain ofthese composite materials are produced from copolymer latexes andfibers. These are the materials to which the present invention relates.With regard to reinforcement, the advantage of cellulose, in particularparticles of microcrystalline cellulose, has already been recognized,for the reinforcement of polymers from using their solutions, forexample, the aqueous solutions of carbamide resins mentioned in WO93/10172, or else for the production of compositions for nail polishes(U.S. Pat. No. 4,891,213) of which the secondary but importantproperties such as transparency or luster of the composite have beenassessed. Also envisaged has been the filling or reinforcing withcellulose by the ordinary methods of compounding of thermoplastic resins(for examples see: Composite Systems from Natural and SyntheticPolymers, by Kalson et al. in Materials Science Monographs, 36, Elsevier1986, or else Future Prospects for Wood Cellulose as Reinforcement inOrganic Polymer Composites, by Zadorecki et al. in Polymer Composites,10/2, p. 69, 1989).

DISCLOSURE OF THE INVENTION

It has now been found that it is possible to produce composites ofcompletely unexpected quality consisting of a thermoplastic polymer anda reinforcement of individualized cellulose microfibrils, with as meansof production, latexes incorporating said cellulose microfibrils. Forthe convenience of language, these latexes will be described in theshortened form of reinforced latexes.

In the sense of the present invention, individualized cellulosemicrofibrils is understood to mean forms of cellulose which are presentin the form of more or less rigid elements, with an average lengthgreater than a micrometer, whose diameter is between approximately 2-30nm, and preferably greater than 7 nm, with a aspect ratio, that is tosay the length/diameter ratio which is always greater than 60, and whosedegree of crystallinity is greater than 20%, and preferably greater than70%.

Generally, cellulose is present in the form of a hierarchy ofstructures. The cellulose molecules are always biosynthesized in theform of microfibrils, which are in turn assembled into fibers, films,walls, etc. The cellulose microfibril can be considered to be animportant structural element of natural cellulose. It consists of anassembly of cellulose chains whose average degree of polymerization isgreater than 1,000 and whose degree of perfection in their parallelorganization is expressed in its crystallinity percentage. It isobtained from crude cellulose whose content with respect to the dryweight of the cell walls of which it constitutes the reinforcementranges from 30% (parenchymal cellulose) to 95% (tunicin cellulose). Itis therefore necessary to apply a dilaceration, bleaching and cleansingtreatment to the cellulose raw material in order to obtain a crudecellulose, and then to obtain the microfibrils from it by powerfulshearing in a homogenizer. The plant cellulose microfibrils areassociated together in a parallel manner in the secondary walls ofinterlaced in a disordered manner in the primary walls. The dissociationof the secondary walls is difficult; in contrast, in the primary walls,it is much easier. The parenchyma is an example of a tissue onlycontaining the primary wall. A model for treatment of animal celluloseis given in Examples 1 and 1bis for obtaining tunicin microfibrils. Forobtaining parenchymal microcellulose, it is possible to apply thetreatments recommended by Weibel (U.S. Pat. No. 4,831,127) for obtainingcrude cellulose.

All the microfibrils do not develop the quality of reinforcement whichis currently looked for, or at least do not develop it to the levelrecognized in the invention. The phenomenon of reinforcement comes fromthe fact that the microfibrils are dispersed in the polymer matrix,within which it organizes itself into a sort of lattice whose unit celldepends on their weight or volume fraction and on their dimensionalcharacteristics. This property is connected with conditions of form:their diameter and their length which is assessed rather in its ratio tothe diameter via a aspect ratio. This property is very greatly dependenton the individuality of the microfibrils, which can be seen clearly inthe microscopic images (see, for example, FIG. 1) but more simply byobservation that their aqueous suspensions at a concentration of a fewpercent are colloidal. This property of reinforcement is also connected,although to a lesser degree, with their rigidity, which is itselfstrictly connected with their crystallinity, whose value increases astheir surface area/volume ratio decreases. This crystallinity isestimated in a well-known way by examination of the X-ray diffractiondiagrams. The important corollary of the dependence of the reinforcementproperties of the microfibrils is that it is considerably altered bytheir aggregation. The microfibrils which can be used for the inventionare distinguished in this from what are ordinarily calledmicrocrystalline celluloses, which result from hydrolysis of wood orcotton cellulose, particularly of its hydrochloric hydrolysis, of whichthe degree of polymerization is already clearly lower, and which aboveall are not individualized; microcrystalline celluloses which, when theyundergo a suitable treatment for individualizing their elements, onlyprovide microcrystals which, even if they more or less still have thediameter of the starting cellulose, are much shorter, for example,approximately 100 nm for wood cellulose (such is the case, for example,of the celluloses used by Boldizar et al., Prehydrolyzed Cellulose asReinforcing Filler for Thermoplastics, Intern. J. Polymeric Mater.,1987, Vol. 11, 229-262).

For proper execution of the invention, it is desirable for thecharacteristics of the microfibrils revealed above to be exactlyproduced. The microfibrils which can be used for the invention generallyconsist of a series of microcrystals separated by zones of amorphouscellulose, the flexibility that they have coming, on one hand, from thelength of the microcrystals, and on the other hand, from the presence ofthe amorphous intermediate segments. This definition which has beengiven for the microfibrils according to the invention also includes thevery long cellulose monocrystals which are obtained with a aspect ratiogreater than 60 by acid hydrolysis of natural cellulose fibers orfibrils, as is the case of tunicin. There are possibilities forbalancing these characteristics; thus, long microfibrils with a certainflexibility may still be acceptable for the invention, as long as thisdoes not hinder their individuality, or else microfibrils with a smalldiameter, which, at comparable weight content with respect to that ofmicrofibrils with a larger diameter, compensate for their lack ofrigidity by a larger density in number and the formation of a densernetwork. These are choices which are up to the expert in the field who,in the particular cases presented to him, always knows how to balancethe advantages and disadvantages, including the economic advantages anddisadvantages, of each solution. The indications which follow will helpin his choices.

The sources of microfibrils are diverse. The plant parenchyma providesmicrofibrils with diameters of 2-3 nm; those of wood are approximately3.5 nm. The long cellulose microfibrils of bacterial origin havediameters of approximately 5-7 nm. The microfibrils of animal origin,and in particular those which can be obtained from tunicin, whichconstitutes the major part of the envelope of marine animals belongingto the family of the Tunicata (for example, the edible species ofHalocynthia roeretzi or Halocynthia aurantium of Japan or Microcosmusfulcatus of the Mediterranean--the sea squirts) have a diameter ofapproximately 10-20 nm. Others, also with a larger diameter, can betaken from algae with cellulose-containing walls.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of tunicin microfibrils;

FIG. 2 is a graph showing the change of the real shearing modulus G' asa function of temperature;

FIG. 3 shows reinforcement obtained by different types of cellulosereinforcements; and

FIG. 4 is a graph of viscosity Pa.s as a function of the pulsation inradians/second.

The tunicin microfibrils, whose image is given in FIG. 1, correspondcompletely to this definition of the microfibrils according to theinvention. They contain few defects and can be considered to be truemicrocrystals to which there is agreement in attributing an elasticmodulus on the order of 130 GPa, which should give the level of breakingstress values on the order of 13 GPa for a microfibril.

Parenchymal cellulose is present in the form of long microfibrils whosediameters are between 2-3.5 nm, which are organized in a disorderedmanner in the cell walls of primary type. Certain ones of thesemicrofibrils are associated in bundles of 10-20 units; others areindividual.

The cellulose microfibrils of bacterial origin have a very high aspectratio, and their crystallinity is lower.

The cellulose microfibrils are used according to the invention in theform of aqueous dispersions as produced by homogenizers. It can occur,and even rather frequently, that the suspensions which are obtained inthis way are flocculent, and therefore that the microfibrils lose theirindividuality in them. It is then necessary to give them a stabilizationtreatment. Thus, the process for preparation of microfibrils asdescribed in the international application WO 93/10172 consists ofcombining disintegration of the cellulose, subjecting it to a powerfulhomogenizer and an acid treatment capable of providing the microfibrilswith electric surface charges, without consequently modifying the orderof magnitude of the initial degree of polymerization of the cellulose,for example, a treatment with sulfuric acid or phosphoric acid. It ispossible to improve the dispersion of the aqueous suspensions thusobtained by subjecting them to ultrasound.

The suspensions with a concentration of up to 0.3% microfibrils aretranslucent. Observation between two crossed polarizers with stirring ofthe suspensions reveals the presence of numerous birefringent areascorresponding to an ordering in the form of liquid crystals. These areasof birefringence become difficult to observe in suspensions withconcentrations greater than 0.6% because of their opaqueness. Thesuspensions of cellulose microfibrils also have remarkable rheologicalproperties. Their viscosity is already quite considerable forconcentrations on the order of 1-2%, and certain ones can have athixotropic behavior. Such suspensions can be used directly for thepreparation of latexes called "reinforced latexes" which will now bespoken of.

In the sense of the present invention, "reinforced latexes" isunderstood to mean aqueous compositions which contain at the same time,in suspension, an amorphous thermoplastic polymer and individualizedcellulose microfibrils, the percentage of microfibrils with respect tothe polymer matrix being 15% or less and even preferably less than 10%.They are obtained very simply by mixing with stirring the two aqueousmedia, one, the latex containing the polymer spheres, and the other, theaqueous suspension of cellulose microfibrils, in the desiredproportions. Their main value is that they are a very convenient vehicleor the material constituted by the final result of their evaporation andwhich is a polymer composition loaded uniformly and regularly withindividualized cellulose microfibrils whose mechanical andthermomechanical properties are absolutely remarkable and unexpected(these materials will be described subsequently under the name ofpolymer/microfibril composite materials). Besides this role ofreinforcement of the polymer matrix, the microfibrils provide thereinforced latex itself with a very considerable thickening function, inthe aqueous compositions such as paints, inks, varnishes, compositionsfor aqueous adhesives and ground surface coverings. The polymer latexeswith which the reinforced latexes of the invention are produced consistof particles of thermoplastic polymers, in the form of spheres, incolloidal dispersion in water. For certain needs which the invention canmeet, for example, the formulation of paints, the formation of a film bycoalescence is advantageously between -40° C. and +90° C., but otheruses can call for thermoplastics whose T_(g) values are outside theselimits. These polymers can be of quite variable chemical composition. Ofparticular interest here are butyl polyacrylate, polystyrene, and theircopolymers, but this is in no way a limitation of the invention whichcan without difficulty be extended to other polymer latexes, particularto the vinyl latexes. The corresponding latexes are obtained by thetechniques of emulsion polymerization which are well known to the expertin the field. They are industrially available.

From these reinforced latexes, various types of composite materials areeasily produced, to which the present invention also relates, accordingto an operation which in its principle is none other than evaporation ofthe latex, an operation which is extraordinarily simple if one comparesit with the traditional method of dispersion of fibers in a polymermass. The polymer/microfibril composite materials, when theirmicrofibril content does not exceed 2% and when they are examined insmall thicknesses (approximately 2 mm), do not display any difference inappearance with respect to the polymer matrix, which is detectable bythe naked eye or even by the optical microscope in ordinary light. Thisis not true of their mechanical properties. The microfibrils, even in asmall percentage, provide a remarkable reinforcing effect at small aswell as at large deformations, and this effect is quite unexpectedlymuch greater than that produced by other types of cellulose structures(wood pulp, microcrystalline cellulose, etc.). From the physicalstandpoint of the materials, one observes no particular modification ofthe glass transition temperature, but the introduction of the cellulosemicrofibrils is expressed by an increase of the relaxation modulus indynamic mechanics, an increase of the slope at the origin, in particularat high temperature, and an increase of the stress equivalent to theplasticity reversal point. This stress at the flow threshold increasesgreatly with the percentage of microfibrils. For example, it goes from80 MPa for a nonreinforced film to 120 MPa for film containing 6%tunicin microfibrils. Which means in practice that the objects producedin this way can withstand much greater stresses without undergoingirreversible deformations. The composites according to the inventionalso have better stability at high temperature (in the diagrams ofmodulus values as a function of temperature, appearance of "rubber-like"plateaux which can be maintained at temperatures up to 225-230° C). Inpractice, the rubber-like modulus of the polymer is multiplied by 100with a load of 6% microfibrils. These modifications are reallyextraordinary and so unlike what is known in prior art that the modelsordinarily used for calculating the elastic modulus or shearing modulusof the composites (Halpin-Kardos model, J. C. Halpin and J. L. Kardos,Moduli of Crystalline Polymers Employing Composite Theory, Journal ofApplied Physics, 43, 1972, 5, 2235-2241), or Tsai-Halpin model,(mentioned by Boldizar, above) cannot be used for the compositematerials containing microfibrils according to the invention (withtunicin microfibrils, it would be necessary to introduce into the modelform factors with a value 25 times greater than the experimentalvalue!). In the application of the invention, the correspondingcompositions contain less than 15% microfibrils in the sense of theinvention, and preferably less than 10%.

It is thus possible to form thick films or objects by simpleevaporation, by pouring the reinforced latex into a mold with anantiadhesive coating in order to allow for easy unsticking of thesecomposites which have a high capacity to adhere. The film forming isthen done in an oven, preferably at a temperature of approximately 30°C. The evaporation must occur very slowly in order to prevent untimelydrying on the surface; for this, the humidity is maintained close to100%, for example, under a perforated cover, and the operation lastsapproximately fifteen days.

It is then possible to form objects made of polymer/cellulose fibercomposites by lyophilization of the corresponding "reinforced latex",and then hot compression of the lyophilized product. This process ofoperation gives composites whose mechanical properties, although lowerthan those of the "evaporates," are remarkable for the low percentagesof reinforcement with which one is operating. It is also possible toconsider extruding the lyophilized product prepared with higherpercentages of reinforcement. The process is particularly suitable forthe production of very small structures, for example, connectors, inwhich the size of the cellulose microfibrils has no influence on theoverall homogeneity of the part. The reinforcement consisting of tunicinmicrofibrils is preferable in this case because of their aspect ratioand their crystalline nature.

It is possible to obtain powders of composite material by lyophilizationof the latex-cellulose mixture, according to the techniques which areknown to the expert in the field. The powders thus obtained are tovarying degrees compact depending on the glass transition temperature ofthe polymer matrix. They can be used as they are or else transformedinto rod by extrusion. Powders and rods can in turn be used for theproduction of plates, films, or objects by compression or injection. Itis also possible to formulate hot melts (hot melts) out of them.

The most direct application of the "reinforced latexes" is without adoubt the formulation of paints and products of the same type, namelyinks, varnishes, adhesives, compositions for ground surface coverings,etc.

It offers various advantages, beginning with that of the possibility ofusing a polymer latex with a glass transition temperature lower thanthose ordinarily used. For example, by taking a latex with a glasstransition temperature of 0° C. instead of 20° C. (usual T_(g) ofpaints), one facilitates film forming (coalescence of the spheres oflatex) at room temperature while maintaining good mechanical propertiesand thermal stability thanks to the addition of the cellulosemicrofibrils. This addition also allows one to benefit from a greatincrease of viscosity without the need for external viscosity agents (orat least limiting their quantities) which, when maintained in the filmafter evaporation, are damaging to its properties and to its properstorage. One observes moreover, and this is very much esteemed, that thepaints formulated with the reinforced latexes of the invention have alengthened recovery time and that the dried paint has a betterresistance to abrasion.

EXAMPLE

The following examples will make the invention better understood.

Example 1

The example relates the preparation of microfibrils carrying sulfateloads, from tunicin.

After having roughly cleaned the pieces of sea squirt envelope, thepieces are put in 500 mL of a 5% aqueous solution of potash (KOH) forone night. They are then washed and whitened for 6 h at 80° C., withchanging of the bath every 2 h. This bath is composed of 300 mL of achlorite solution (17 g of NaClO₂ in 1 L of distilled water) mixed with300 mL of an acetate buffer solution (27 g of NaOH added to 75 mL of CH₃COOH and completed to 1 L with distilled water). This whiteningtreatment is repeated 3 times; it makes the pieces of sea squirtscompletely white.

The pieces of cellulose are then disintegrated in a Waring Blender mixerfor 20 min; the concentration in terms of pieces is approximately 5% inthe distilled water. One thus obtains a flocculent aqueous suspension ofwall fragments, which is diluted to approximately 1% and introduced insuccessive cycles into a Gaulin 15N8TA mechanical homogenizer. Thepressure of the apparatus is raised to 600 bar in stages in order toavoid blocking of the apparatus by the coarser fragments of cellulose.One should monitor the temperature rise taking care to limit it to 70°C. After approximately fifteen cycles, one obtains a homogeneoussuspension containing small aggregates of fibers. A very simple test ofthe effectiveness of the operation consists of observing the increase ofthe thickness of the product. As an indication, the desired result isreached when the consistency of Vaseline is obtained with suspensionwith a concentration of approximately 2% cellulose.

The suspension coming from the homogenizer is then treated with sulfuricacid, in a proportion of 300 mL of concentrated sulfuric acid (95%) per450 mL of the suspension coming from the homogenizer. The whole ismaintained at 60° C. for 20 min. This suspension is then filtered usinga sintered glass (porosity 1) in order to eliminate the coarseaggregates, after which the cellulose fibrils are retained using afilter with porosity of 4. One washes with distilled water and then withsoda NaOH (0.1%) to neutrality of the suspension, and then again withdistilled water. The cellulose is then deposited on the filter in theform of an aqueous pulp with a viscous consistency. It is redispersed inwater; the suspension is homogenized using a magnetic stirrer, and thensubjected to ultrasound (Branson Sonifier B12) for approximately 5 min.The final suspension is ready for use, suitably homogeneous,nonflocculent, and stable for several weeks.

Example 1bis

The example relates the preparation of microfibrils carrying phosphateloads, from tunicin.

One proceeds as in Example 1 with the whitening of the sea squirts andthe homogenizer treatment. 18 g of the 1% suspension coming from thehomogenizer are then added to the phosphorylation medium consisting of50 g of urea dissolved at 50° C. in 85% orthophosphoric acid. Themixture is then heated to 140° C. in an oil bath for 15-25 min. Theprotocol of cleaning, recovery, and dispersion of the microfibrils isthe same as that of Example 1.

This "phosphoric" mode of preparation is preferable to the "sulfuric"mode of Example 1 for microfibrils other than those of tunicin and whichdo not have as good a resistance to acid hydrolysis.

Example 2

Preparation of reinforced latexes

Reinforced latexes with various percentages of microfibrils wereprepared from suspensions of tunicin microfibrils with a dry extractcontent of 0.68% and a latex with a dry extract content of approximately50% formed by emulsion polymerization of 34% styrene, 64% butylacrylate, 1% acrylamide, and 1% acrylic acid; the corresponding polymerhas a glass transition temperature T_(g) of +0° C. The correspondingreinforced latexes result from their careful mixture with suspensions ofcellulose microfibrils in proportions such that the percentage of thereinforcement in the copolymer is at the intended values. For example,one forms systems whose dry material contains approximately 6%microfibrils by carefully mixing 18.5 parts of latex and 81.5 parts ofthe suspension of microfibrils.

Example 3

Elastic moduli of the composites

From the latex of the preceding example, reinforced respectively by 6,3, 1, and 0% tunicin microfibrils, and according to the technique ofthick films by evaporation described above, small parallelepipeds wereformed (length 15-20 mm, width 6-7 mm, thickness 0.5-2 mm), which weresubjected to a dynamic analysis with the torsional pendulum (MetravibInstruments mechanical analyzer), in a temperature range from 200-350 K.(for a more detailed explanation on the viscoelastic behavior of theSty-ABu copolymer, refer to J.-Y. Cavaille, R. Vassoille, G. Thollet, L.Rios, and C. Pichot, Structural Morphology of Polystyrene-polybutylAcrylate Polymer--Polymer Composites Studied by Dynamic MechanicalProperties, Colloid & Polymer Science, 269 (1991), 248-258, and for thetechnology of the Metravib mechanical analyzer to J.-Y. Cavaille et al.,A New Tool for Mechanical Spectrometry Analysis: the MicromechanicalAnalyzer, Spectra 2000, 16, No. 113, 1988, 37-45). It allows one toobtain curves of the moduli which are characteristic of the composite asa function of the temperature, in particular its real shearing modulusG' which is associated with the elastic energy stored in the materialduring deformation, the imaginary modulus G" which is associated withthe viscous character and therefore with the energy dissipated duringthe test, and the magnitude tan(φ)=G"/G', tangent of the loss angle, isthe interior friction coefficient characterizing the ability of thematerial to dissipate energy when it is subjected to a cyclic stress.FIG. 2 represents the change of the real shearing modulus G' as afunction of the temperature. The dynamic behavior of the testedcomposite samples is typical of that of a polymer, with a drop of theshearing modulus during the glass transition, framed by two plateaux,one at the low temperatures (T<T_(g)) corresponding to the glass domainand the other at the high temperatures (T>T_(g)) corresponding to therubber-like domain. One observes that the glass transition temperatureT_(g) is practically not affected by the load of microfibrils. At thetemperatures higher than T_(g), the reinforcing effect is remarkable, ifit is judged by comparison with the modulus of the polymer alone whichdrops to 10⁵ Pa. The relaxation modulus of the film containing 6%tunicin microfibrils is more than 100 times greater than the relaxedmodulus of the pure matrix. Moreover, this modulus remains perfectlyconstant up to 500 K., the temperature at which the cellulose begins tobreak down. Contrary to the case of the pure matrix, the polymer chainsdo not yield with the temperature. The thermal stability of the materialis thus improved.

Example 4

According to the process described in Example 3 above, tests pieces weresubjected to the dynamic analysis, pieces with the same geometry, butproduced according to the technique of the pressed powders with latexeswhich differ from those of Example 2 in that they are formed by emulsionpolymerization of 49% styrene, 49% butyl acrylate, 1% acrylamide, and 1%acrylic acid, and whose temperature of glass transition T_(g) is +20° C.The curves of FIG. 3 allow one to compare the reinforcement obtained bydifferent types of cellulose reinforcements. The composites testedcontained about 6% reinforcement: tunicin microfibrils, bacterialcellulose microfibrils prepared in the laboratory, microcrystalline woodcellulose (these last two were obtained by application of the treatmentof Example 1, but applied respectively to a bacterial cellulose and acommercial microcrystalline cellulose). One observes, in the diagram,the considerable power of reinforcement of the tunicin microfibrils,compared with that which is much more modest of the wood cellulosefibrils which is attributed to their association in the form ofnonindividualized aggregates and to their very low aspect ratio, orcompared with that of the bacterial cellulose fibrils which are long butdevoid of rigidity.

Example 5

Viscosity of the reinforced latexes

The latex viscosity was measured with a Carri-Med CSL 100 plane-coneflow meter with imposed stress, functioning dynamic flow. FIG. 4 reportsthe results on a graph of viscosity Pa·s as a function of the pulsationin radians/second. The control is the acrylic latex of Example 4, whichis compared with the same latex with addition, on one hand, of 1% of themicrocrystalline cellulose, and on the other hand, of 1% tunicinmicrofibrils according to the invention as obtained according to Example1.

Although the invention has been described in conjunction with specificembodiments, it is evident that many alternatives and variations will beapparent to those skilled in the art in light of the foregoingdescription. Accordingly, the invention is intended to embrace all ofthe alternatives and variations that fall within the spirit and scope ofthe appended claims. The above references are hereby incorporated byreference.

What is claimed is:
 1. A composition comprising an amorphousthermoplastic polymer matrix and a cellulose filler, the cellulosefiller having from 1% to less than 15% individualized cellulosemicrofibrils each formed of a series of microcrystals separated by zonesof amorphous cellulose; said microfibrils having an average lengthgreater than a micrometer, a diameter between about 2-30 nm, an aspectratio greater than 60, and a degree of crystallinity greater than 20%;wherein said microfibrils are selected from the group consisting oftunicin, algae with cellulose-containing walls, parenchymal, andmixtures thereof; and wherein the glass transition temperature of thecomposition is substantially the same as said matrix but introduction ofsaid microfibrils expresses an increase of relaxation modulus in dynamicmechanics, an increase of slope at the origin, in particular at hightemperature, and an increase of stress equivalent to plasticity reversalpoint.
 2. A composition according to claim 1, wherein the microfibrilsare tunicin microfibrils.
 3. A composition according to claim 1, whereinthe microfibrils are microfibrils of algae with cellulose-containingwalls.
 4. A composition according to claim 1, wherein the microfibrilsare parenchymal microfibrils.
 5. An aqueous composition comprising alatex polymer and a cellulose filler, the cellulose filler consists ofmicrofibrils according to claim 1, in a stable suspension andindividualized in the composition.
 6. An aqueous composition accordingto claim 5, wherein the polymer latex is a latex of a thermoplasticpolymer with a glass transition temperature between -40° C. and +90° C.7. An aqueous composition according to claim 5, wherein the microfibrilsare stabilized by the presence of surface charges.
 8. An aqueouscomposition according to claim 7, wherein the microfibrils carry surfacecharges consisting of sulfate ions.
 9. An aqueous composition accordingto claim 7, wherein microfibrils carry surface charges consisting ofphosphate ions.
 10. Compositions according to claim 5, wherein themicrofibrils are tunicin microfibrils.
 11. Compositions according toclaim 5, wherein the microfibrils are microfibrils of algae withcellulose-containing walls.
 12. Compositions according to claim 5,wherein the microfibrils are parenchymal microfibrils.
 13. Films of thecomposition according to claim 1, wherein they are obtained byevaporation of stable aqueous composition of polymer latex and aqueoussuspension of cellulose microfibrils.
 14. Powders of the compositionaccording to claim 1, wherein they are obtained by lyophilization of astable aqueous composition of polymer latex and aqueous suspension ofcellulose microfibrils.
 15. Rods of the composition according to claim1, wherein they are obtained by extrusion of a powder of claim
 14. 16.Plates of the composition according to claim 15, wherein they areobtained by pressing of the powder of claim
 14. 17. Method of makingpaints, inks or varnishes comprising formulating them with the aqueouscomposition according to claim
 5. 18. Method of making aqueous adhesivesor composition for ground surface coverings comprising formulating themwith the aqueous composition according to claim
 6. 19. Manufacturing ofobjects of the composition according to claim 1 comprising evaporationof lyophilization of a stable aqueous composition of polymer latex andaqueous suspension of cellulose microfibrils.
 20. Manufacturing ofobjects by pressing or injection respectively of powders according toclaim
 14. 21. Method of preparing hot melts comprising utilizing powdersaccording to claim
 14. 22. A composition according to claim 1, whereinthe crystallinity of said microfibrils is greater than 70%.
 23. Acomposition according to claim 1, wherein it contains less than 10%microfibrils.
 24. Plates of the composition according to claim 15,wherein they are obtained by pressing of the rods of claim
 15. 25.Method of manufacturing rods according to claim
 15. 26. Method ofpreparation of hot melts comprising utilizing the rods according toclaim
 15. 27. Composition according to claim 1, wherein the polymermatrix is a vinyl latex.
 28. Composition according to claim 1, whereinthe polymer matrix is butylpolyacrylate, polystyrene or copolymersthereof.